As for the valve device forming a ventilation flow channel of the fuel tank, there is a valve device including an outer sleeve, an inner sleeve, and a float, wherein the float sits on a valve opening formed in an upper portion of the outer sleeve at an elevated position (see Patent Document 1). The outer sleeve includes a connection portion to a conductor at an upper portion of the valve opening, and there is provided a seal member for improving a seal property at a sitting time at an upper portion of the float.
As for such valve device of the Patent Document 1, in addition to the seal member, a seal member for sealing between the connection portion of the outer sleeve and the conductor is separately required.